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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #365976

Title: Biochar surface oxygenation by ozonization for super high cation exchange capacity

item KHAREL, GYANENDRA - Old Dominion University
item SACKO, OUMAR - Old Dominion University
item FENG, XU - Virginia Tech
item MORRIS, JOHN - Virginia Tech
item Phillips, Claire
item Trippe, Kristin
item KUMAR, SANDEEP - Virginia Tech
item LEE, JAMES - Old Dominion University

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2019
Publication Date: 9/4/2019
Citation: Kharel, G., Sacko, O., Feng, X., Morris, J., Phillips, C.L., Trippe, K.M., Kumar, S., Lee, J. 2019. Biochar surface oxygenation by ozonization for super high cation exchange capacity. ACS Sustainable Chemistry & Engineering. 7(19):16410-16418.

Interpretive Summary: Biochar is a carbon-rich material made from low-value biomass that is added to soils for agricultural and environmental applications. Although biochar has been used for several centuries to improve soil function and fertility, it is difficult to predict how biochar will interact with soil and plants to influence plant performance. Moreover, while some studies show improvements in crop production and soil fertility following biochar amendment, analyses of data combined from multiple studies also demonstrate no improvements or declines in crop production in a large fraction of studies. In general, biochar that has been composted or “aged” in the soil is more effective at increasing yields than fresh biochar. One hypothesis that explains the disparity between aged and fresh biochars is that aged biochars tend to have more oxygen functional groups on their surface, which increases their cation exchange capacity (CEC). CEC is a measure of a soils ability to retain plant nutrients. Increased CEC directly leads to increased soil fertility, water holding capacity, and an ability to resist pH change. Therefore, many initiatives seek to alter the biochar production process to improve the overall structure and function of biochar particles. In the current study, a breakthrough process called ozonization dramatically improves biochar CEC value by a factor of 7.5 is reported. This process increases CEC through surface oxygenation by exposing biochar to ozone. The results of our study indicate that ozonization is an effective method to increase oxygen functional groups and CEC while significantly lowering biochar pH. Future studies will focus on describing the effects of using ozone treated biochars on plant productivity in several cropping systems.

Technical Abstract: Biochar cation exchange capacity (CEC) is a key property central to better retain soil nutrients and reduce fertilizer runoff. This paper reports a breakthrough progress in dramatically improving biochar CEC value by a factor of 7.5 through biochar surface oxygenation by ozonization. The CEC value of the untreated biochar was measured to be anywhere between 14 and 17 cmol/kg. A 90-minutes dry ozonization treatment resulted in a dramatically increased biochar CEC value of 109~152 cmol/kg. Simultaneously, the biochar ozonization process resulted in dramatic reduction of biochar pH from 9.82 to as low as 3.07, indicating the formation of oxygen-functional groups including carboxylic acids on biochar surfaces. Using the techniques of X-ray photoelectron spectroscopy, the formation of oxygen-functional groups including carboxylic acids on biochar surfaces have now, for the first time, been observed at a nanometer molecular scale upon biochar surface oxygenation through the ozonization treatment. The molar O:C ratio (0.31:1) on ozonized biochar surface as analyzed by XPS was indeed significantly higher than that (0.16:1) of the control biochar surface. Surprisingly, the molar O:C ratio from the Elemental Analysis data also showed an increase from the non-ozonized sample (0.077:1) to the dry-ozonized sample (0.193:1). Fourier-transform infrared spectroscopy analysis also showed an increase in the content of oxygen-functional groups in the form of carbonyl groups on biochar surfaces upon ozonization, which can also produce certain amount of oxygenated biochar molecular fragments that may be solubilized by liquid water for special applications such as to unlock phosphorous from insoluble phosphate materials in soils.